The invention relates to the field of electrical power transmission and distribution and the need to insulate electrical power lines from short circuits caused by birds and other animals. More particularly, the invention relates to an insulation method and material for coating selected portions of the structures supporting wires such as electrical transmission lines and related components.
Long-distance electricity transmission is typically carried with high voltage conductors. Higher voltages reduce resistance power loss, and line voltage for long distance lines is stepped up with generating stations at selected locations. Transmission lines traverse large regions and require numerous support towers. The conductors in high tension powerlines are typically uninsulated because of the cost and additional weight of insulated versus uninsulated conductors.
Electric poles and towers provide attractive roosts for birds, particularly in treeless regions. If the wings of a bird simultaneously contact a transmission line and another object such as an adjacent wire, support tower or tree, the resulting electrical short-circuit can kill the bird and also damage the power system. The electrical short can further cause electrical system damage resulting in power outages. Because large (and typically protected) birds are more susceptible to such incidental contact, electrocution hazards disproportionately affect large bird species such as raptors.
The variety and number of proposed solutions for repelling birds and other animals from electrocution risks highlights the persistence and magnitude of the problems created by such undesirable intrusion. Many different types of scarecrows and other moving devices have been developed to repel birds. For example, U.S. Pat. No. 4,131,079 to Rousseau et al. (1978) disclosed a wind operable scarecrow. U.S. Pat. No. 4,185,581 to Tilton (1980) disclosed a weight responsive perch for scaring birds. U.S. Pat. No. 4,597,357 to LeMessurier (1986) disclosed a movable aluminium sheet for scaring birds. U.S. Pat. No. 4,598,660 to Konzak (1986) disclosed an air gun for releasing a gas stream to scare birds. U.S. Pat. No. 4,656,770 to Nuttle (1987) disclosed a tiger cat weathervane. U.S. Pat. No. 4,937,988 to Gratton et al. (1990) disclosed a barrier to birds formed with monofilament line. U.S. Pat. No. 4,962,619 to Chatten (1990) disclosed a coiled wire having movable elongate flaps. U.S. Pat. Nos. 5,343,651 (1994) and 5,452,536 (1995) to Chatten disclosed a rotating carriage propelled by wind for repelling birds. U.S. Pat. No. D0359099 to Sugimoto (1995) disclosed a windmill for scaring birds, and U.S. Pat. No. 5,713,160 to Heron (1998) disclosed a retractable bird deterring device.
In addition to moving devices, various physical structures have been developed to discourage birds from roosting on structures. U.S. Pat. No. 3,407,550 to Shaw et al. (1968) disclosed spikes attached to a mounting structure. U.S. Pat. No. 4,269,008 to Assouline (1981) disclosed optical pyramid structures for generating prisms to scare birds. U.S. Pat. No. 4,845,307 to Cumming et al. (1989) disclosed a high density polyethylene wildlife guard for shielding electrical conductors at the point of attachment to an insulator bushing, and further described prior difficulties in creating an effective physical guard for such conductors. U.S. Pat. No. 5,058,335 to Richter (1991) disclosed flexible plastic fingers attachable to a wire for deterring birds. U.S. Pat. No. 5,092,088 to Way (1992) disclosed a bird deterring device having retractable wires. U.S. Pat. No. 5,253,444 to Donoho et al. (1993) disclosed a base having spikes for repelling birds, and U.S. Pat. No. 5,433,029 to Donoho et al. (1995) disclosed a channel member for clamping onto an electrical wire. U.S. Pat. No. 5,400,552 to Negre (1995) disclosed a channel base having multiple spikes for repelling birds. U.S. Pat. No. 5,454,183 to Antonini et al. (1995) disclosed a resilient base engaged with two wire mesh sections for repelling birds. U.S. Pat. No. 5,691,032 to Trueblood et al. (1997) disclosed a base having a plurality of bird repelling slots and arms extending from the base. U.S. Pat. No. 5,606,830 to Townsend, Jr. et al. disclosed grid fencing panels for attachment to electric cables or wires. U.S. Pat. No. 6,250,023 to Donoho (2001) disclosed a base having spikes for discouraging birds.
Other bird repelling concepts use electricity or magnetics to discourage bird intrusion. U.S. Pat. No. 5,255,896 to Letarte et al. (1993) disclosed an electrified fence for repelling birds. U.S. Pat. No. 5,353,543 to Teraoka (1994) disclosed a rotating magnetic field for repelling birds. U.S. Pat. No. 5,666,767 to Ohba (1997) disclosed a magnet activated by the weight of a bird to generate a bird discouraging magnetic field. U.S. Pat. No. 5,648,641 to Guthrie (1997) disclosed an electrostatically charged animal barrier. U.S. Pat. No. 5,884,426 to Ishida (1999) disclosed a wind movable magnet for generating a bird discouraging magnetic field. U.S. Pat. No. 6,006,698 to Negre (1999) disclosed electrified rails for generating vibrations for discouraging birds. U.S. Pat. No. 6,016,100 to Boyd et al. (2000) disclosed a device for generating an oscillating ultrasonic animal deterrent signal. U.S. Pat. No. 6,250,255 to Lenhardt et al. (2001) disclosed techniques which pulsated microwaves or sound waves to repel birds.
Shield and cage devices have been specifically designed to restrict birds and other animals from short-circuiting electrical leads. For example, U.S. Pat. No. 4,845,307 to Cumming et al. (1989) disclosed a high density polyethylene skirt for covering insulator bushings. U.S. Pat. No. 5,153,383 to Whited et al. (1992) disclosed a flexible sheet of PVC material attached with VELCRO strips for shielding electrical equipment. U.S. Pat. No. 6,005,196 to Spillyards (1999) disclosed a spring biased cage for covering an insulator bushing. U.S. Pat. No. 5,864,096 to Williams et al. (1999) disclosed a wildlife guard comprising a disk. U.S. Pat. No. 6,248,956 to Cook et al. (2001) disclosed an annular guard for shielding a high voltage insulator.
Materials have been developed to resist animal damage. In one example, U.S. Pat. No. 5,997,894 to Blum et al. (1999) disclosed a coating composition resistant to animals which comprised a hard, ceramic particle laden material for protecting underground wires and cables from rodents.
Various chemicals have been used to repel birds from an area or structure. U.S. Pat. No. 3,734,875 to Sekuler (1973) disclosed an aerosol bird repellent. U.S. Pat. No. 4,693,889 to Chirchirillo et al. (1987) disclosed a bird repellent composition formulated to limit stains to the structure treated. U.S. Pat. No. 5,196,451 to Greig-Smith et al. (1993), U.S. Pat. No. 5,296,226 to Askham (1994), and U.S. Pat. No. 5,549,902 to Preiser et al. (1996) disclosed other bird repellent compositions.
U.S. Pat. No. 6,226,933 to Nelson et al. disclosed a configurable sheath for protecting structures such as wires wherein the sheath could incorporate passive or active components (such as chemical repellents) for repelling animals such as birds. Nelson et al. disclosed spikes, engaged with a protective sheath, which released a noxious chemical following activation of the spikes by a bird or other animal. Nelson further disclosed that the spikes could be attached to the structure or integrated within a base material attached to the structure.
Another technique using chemical compounds to repel birds was disclosed in U.S. Pat. No. 4,873,082 to Cacioli et al. (1989) wherein a multi-layer coating comprised a brittle, polystyrene protective cover over a tacky, bird repellent layer. The outer layer prevented the accumulation of dust on the inner tacky layer. When the brittle protective cover was disturbed by a bird a noxious, bird repellent composition was released to repel the intruding bird.
The variety and number of these efforts indicate significant problems in the exclusion of birds from undesirable areas, and the inherent difficulties in effectively accomplishing such exclusion. Many of these techniques are expensive to employ and are ineffective in preventing birds from landing in a particular spot. A need exists for an improved method and apparatus capable of resisting electrical wire short circuits deleterious to birds and other animals.